Semiconductor devices, such as integrated circuit (IC) packages, typically include one or more semiconductor devices arranged on a lead frame or carrier. The semiconductor device is attached to the lead frame, typically by an adhesive material or by soldering, and bond wires are attached to bond pads on the semiconductor devices and to lead fingers on the carrier to provide electrical interconnections between the various semiconductor devices and/or between a semiconductor device and the carrier. The device is then encapsulated in a plastic housing, for instance, to provide protection and form a housing from which the leads extend.
Such semiconductor packages typically include a semiconductor chip with a metallization layer formed over the chip to provide conductive paths and the conductive landings for the wire bonds, among other things. The metallization layer is often made up of multiple layers, such as copper, nickel-phosphorus, palladium and/or gold layers, for example. Applying the plastic encapsulation material directly over the metallization layer can result in electrical short circuits between different electrical potentials of the metallization layer, corrosion by and under the metallization, insufficient encapsulation compound and adhesive binding (resulting in delamination of the encapsulation material), etc.
Attempted solutions for such problems have been largely unsatisfactory. For example, a Polyimide coating is sometimes applied on the chip front metallization layer, but this also has disadvantages. For example, the high moisture content of the Polyimides can actually promote corrosion and contamination of the metallization, and the added layer of Polyimide might not provide the desired thermal conductivity. Moreover, the Polyimide material tends to be expensive.
For these and other reasons, there is a need for the present invention.